As imaging techniques for obtaining a depth-direction distance as two-dimensional array information, various methods are being developed, such as a technique utilizing reference light and a stereo distance measurement technique utilizing more than one camera. Particularly, there is an increasing demand for relatively inexpensive products as novel input devices for consumer use in recent years.
An imaging device utilizing microlenses has been known as a technique for obtaining a range image in an indirect manner. This device includes an imaging optical system, an imaging element, and a microlens array having microlenses between the imaging optical system and the imaging element. Light beams that are guided through an area in the lens aperture stop from the same subject point by the imaging optical system and form an image near the surface of the microlens array are redistributed to the pixel areas of the imaging element by the microlenses. The distribution of incident light beams is realized by the differences in incident angle with respect to the microlenses, and the differences in incident angle with respect to the microlenses reflect the range information. Therefore, an image that is focused at a desired range can be reconstructed by performing image processing on pixel signals formed by obtaining the distributed light beams at the respective pixels.
Also, since a desired viewpoint image within the aperture width of the imaging lens can be reconstructed, range image information can be calculated by triangulation from two or more viewpoints. Normally, where the range image information is calculated from arbitrary viewpoints, the range resolution becomes higher in proportion to the focal length of the imaging system and the distance between the viewpoints.
Such an imaging device has a problem that the optical system size and the range resolution is in a trade-off relationship both in the longitudinal direction (the focal length direction) and the lateral direction (the lens aperture direction), and this problem hinders miniaturization of cameras.